This kind of rotary cathode unit is known, e.g., in Patent Document 1. This conventional example has: a cylindrical target which is disposed to lie opposite to a substrate inside a vacuum chamber; a magnet unit which is disposed in an inner space of the target; a cooling medium circulation means for circulating a cooling medium in the inner space of the target; and a driving means for driving the target to rotate. As the magnet unit there is used one having on one surface of a yoke made of a magnetic material and having a length equivalent to a generating line of the target: a central magnet which is disposed to extend along the generating line of the target; peripheral magnets which are disposed on both sides of the central magnet so as to be extended along the central magnet; and corner magnets which bridge the peripheral magnets in a manner to enclose both ends of the central magnet. In this arrangement, the polarity on the side of the substrate relative to the central magnets and to the peripheral magnets and the corner magnets is switched to generate a magnetic field leaking from the surface of the target so that a line to pass through a position in which the vertical composition of magnetic field becomes zero is extended along the generating line of the target, between the target and the substrate, thereby closing like a race-track shape. Further, in the inner space of the target, there is disposed a moving means for integrally moving the magnet unit toward, and away from, the target.
In case the target is sputtered while rotating the target by using the above-mentioned rotary cathode unit, plasma will be generated along the race-track shaped line. Along this line the electrons in the plasma will be moved clockwise or counter-clockwise depending on the polarity of the substrate relative to the central magnets and to the peripheral magnets and the corner magnets. At this time, the electron density is likely to become locally high at the corner portions of the race-track. In this case, as long as the erosion of the target along the generating line of the target is concerned, the amount of erosion on those both sides of the target which respectively lie opposite to the corner portions becomes larger than the amount of erosion at the central portion of the target. A disadvantage occurs in that the target utilization efficiency is remarkably deteriorated.
As a method of eliminating this kind of disadvantage, it is conceivable to change the space between the target and the magnet unit to thereby change the intensity of the magnetic field that leaks from the surface of the target. However, it is impossible to restrain the local erosion at both end portions of the target simply by integrally moving the magnet unit, toward and away from the target, as in the above-mentioned conventional example. On the other hand, it is conceivable to locally weaken, at those corner portions of the magnet unit which give rise to local erosion of the target, the intensity of the magnetic field that leaks from the surface of the target by changing, e.g., the kind of magnet, the arrangement of magnets. However, although the local erosion of the target at the end portions of the target may be restrained by weakening the magnetic field, it has been found that the amount of erosion changes at that portion of the target which is positioned from these end portions toward the inside in the direction of the generating line.